Condenser



C. D. TUSKA April 9, 1929.

CONDENSER Filed Aug. 7, 1.924

INVENTOR 9 BY 9 V/Ml 'ATTORNEYS Patented Apr. 9, 1929.

UNITED STATES PATENT OFFICE.

CLARENCE TUSKA, OF HARTFORD, CONNECTICUT, ASSIGNOB ,,BY MESNE ASSIGll- MENTS, TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE.

V CONDENSER.

- Application filed August 7, 1924. Serial No. 730,710

This invention relates to condensers for radio apparatus and has for its object, more particularly, the provision of means whereby two separate condensers of the rotary plate type may be conveniently and quickly adjusted in balance,-in other words, have the capacities of the two condensers equalized.

Heretofore, in radio apparatus comprising two or more tuned circuits in series, attempts have been made to tune said separate circuits with a single operating member such as a dial knob connected with the rotors of two separate condensers, one condenser being in each of the tuned circuits, While this arrangement enables the capacity of each condenser to be varied simultaneously and to a more or less uniform degree by a single knob, nevertheless, this practice was found objectionable and unsatisfactory due to the fact that it is almost impossible by usual manufacturing methods to make both condensers of equal capacity for tuning the cir- ,cuits simultaneously. As is well known, the capacity of a condenser with a plurality of interleaved plates is the sumof the capacities between each pair of'opposed plates, whereas the capacity betweeneach pair of opposed plates varies inversely as the distan'cebetween them or the thickness ofthe air gap.

ns quently, unless the most elaborate precautions are taken in the manufacture of such condensers, it is practically impossible to make two rotary plate condensers of-exactly the same capacity, at least to the fine 5 degree of exactitude demanded in radio circuits. This is obviously due to the unequal distances between the interleaved plates of one condenser as compared with the distances between the interleaved plates of the other 40 condenser. It would require laboratory work of the highest order to space all of said plates precisely the same distance apart, and at the same time have their surfaces parallel throughout and of the same area such as would be necessary to obtain equal capacity between the two condensers.

[While machine work of such a high degree of precision might be possible, it would be too expensive for ordinary commercial radio sets and the present invention aims at overcoming the necessity of such accurate machine work and at the same time provide a simple and eflicient means for compensating the effect of such slight inaccuracies of spacing between the plates as may be encountered in commercial manufacture and thereby make it possible to adjust two of such condensers to exactly the same capacity.

The full advantages of the improvement will become apparent from the following specification taken in connection with the accompanying drawings, which show the preferred embodiment ofthe invention and in which: 1

Fig. l is an elevation. of two rotaryplate 66 condensers with the rotor plates of each condenser mounted on a common shaft;

Fig. 2 is a section along line 2-2 of Fig.

1 showing an end view of said'plates;

Fig. 3 is a detail section along line 70 of -Fig. 1 showing the adjustable left end bearing for the rotor shaft; and

Fig. 4 is a similar sectional view taken through line 44 of Fig. lshowing the adjustable right end bearing for said rotor shaft.

Referringmore particularly to the drawings, the supporting frame for the two condensers may be of any suitable form and as shown comprises a middle plate or annular s0 rin of insulation 1, a right hand plate of insulation 2 and lefthand plate of insulation 3 connected by suitable tie bolts 4, 5, 6 and 7 in the usual manner. The tie bolts 4 and 5 serve as a common conducting terminal and support for the fixed plates 8 of the left hand condenser and tie bolts 6 and 7 as a common conducting terminal and support for the fixed plates 9 of'the right hand condenser.

The fixed plates are held in spaced relation upon their respective supports in the usual manner and interspaced between the fixed plates'are the rotor plates of the two 0ondensers. The rotor plates 10 of the left hand ,condenser as well as the rotor plates 11 of the right hand condenser are mounted upon In the present case, however, the two condensers shown are designed for use 1n two consecutive grid circuits wherein the rotorplates of each condenser will have a connection through the filament or A battery and consequently it is not necessary to insulate the two sets of rotor plates from each other. It will be understood, of course, that all of said plates arearranged in parallel. relation as shown and that the angular disposition of the rotor and fixed plates is the same for both condensers as shown in Fig. 2.

Referring more particularly to the rotor shaft and bearings therefor, it will be observed that this shaft is mounted so as to be adjust-able longitudinally of its axis which adjustment effects a lateral shift of all of the rotor plates of both condensers. Various forms of adjustable bearings for said rotor shaft may be provided and suitable bearings for this purpose are shown more clearly in Figs. 3 and 4. V The shaft 12 at its right hand end has pinned thereto a spherical faced bearing member 13, turnable in a concave'seat of the sleeve member 14 to provide a self-aligning cone bearing for this end of the shaft. The shaft 12 extends through the hollow portion of said sleeve 1 L preferably with a slight clearance, and may have a dial knob fastened to its outer end (not shown) whereby it may be rotated. 15 and 16 indicate lock nuts, screw-threaded on the exterior of the sleeve 14 whereby said sleeve may be fixed in various adjustments to the right or left with respect to the frame plate 2.

In order to keep the bearing member 13 of said shaft'12 in proper contact with its seat 14 the other end of said shaft 12 is provided with a suitable adjustable end thrust bearing as shown in Fig. 3-. The reduced left end of said shaft 12 extends part way within a sleeve 17 mounted in said frame plate 3. Screw threaded on the outer end of said sleeve 17 is a nut 18 for securing the same in place. An adjustable screw stud 19 is screw threaded into the interior bore of said sleeve 17 with its end in contact with the end of said shaft 12 thereby serving as an end bearing for said shaft. 20 indicates a lock nutfor securing the screw stud 19 in its adjustments. A coil spring 21 surrounding shaft 12 is preferably interposed between a nut 22 which holds the rotor plates on said shaft and said stationary sleeve 17 whereby good electrical contact is obtained between said rotary plates and sleeve 17. The leads from said condensers may be connected as shown, a lead 23 to the sleeve 17, a lead 24 to the terminal 4 and a lead 25 to the terminal 7.

It will be obvious from the above that the rotor shaft 12 together with all the lates carried thereon may be shifted longitudinally to thereby vary the spacing simultaneously and to an equal amount between all of said interspaced rotor plates and the opposed fixed plates. In this way the capacity of each condenser will be changed.

In utilizing such an adjustment, to make the capacities of the two condensers equal, advantage is taken of tlfe fact that since it is commercially impractical to mount all the plates of said two condensers an equal distance apart and to space the rotary plates of each condenser at exactly the same distance from their opposed fixed plates, then it will be certain that in commercial manufacture the opposed plates of each condenser will not be spaced from one another in exact similitude. In other words, exactitude of spacing being commercially impossible, dependence is had on the fact that inexactit-ude is certain to result in the manufacture of two condensers, Inasmuch, then, as the capacity of the two condensers will certainly be unequal to start with due to unequal spacing between opposed plates, a longitudinal adjustment one way or another of said rotor shaft 12 will result in a variation of capacity in both condensers, but such variation will certainly not be in the same proportion. It is to be remembered that the capacitybetween each pair of opposed plates varies inversely as the distance between them and that the total capacity of each condenser is the sum of such several capacities. Nothing but exact similitude in spacing throughout both condensers would cause their totalcapacities to chan e in the same proportion when the rotor shifted laterally as a unit with respect to the fixed plates. For example, the capacity of one condenser will be sure to increase or decrease more than the capacity of the other condenser with the same amount of shift of the rotor plates, due to the initial unequal spacing of the plates in the two condensers. In some cases one condenser may actuallyincrease in capacity while the other condenser decreases in capacity upon such a shift.

The principle stated above can be demonstrated and perhaps rendered clearer by mathematics. In essence the action depends upon the change in capacity when a plate forming one side of a condenser is shifted laterally between two parallel plates connected together and forming the other side of the condenser. These two plates, typifying two adjacent stator plates in the drawing, are at a constant distance apart, so that no matter how the central plate is shifted laterally the sum of the spaces on either side of it remain a constant. This typical three-plate plates are condenser can be considered as two condensers in parallel, one formed by one side plate and the central plate, separated by a distance d; and the other formed by the other side plate and the central plate, separated by a distance d". Since the condensers are in parallel, their capacities are'additive, and by the wellknown approximate formula, the combined capacity s KA KA KA d +11". W W 1Y where A is the area of the plates and K is the specific inductive capacity of the dielectric.

Now let d'+d"=m, which is a constant representing the total spacing of'the outer plates less the thickness of the central plate. And let d d" =E, which we may term the eccentricity of spacing, being zero when the m E m E x-aw)? This last equation shows that 0, the total capacity of the three plate condenser being considered, varies with the eccentricity of spacing of the central plate. When the central plate is exactl in the middle E is zero, and the capacity is at a minimum. When the central plate is shifted transversely the KA ff;

value of E 2 increases, no matter in which direction the shift occurs, and since the denominator of the fraction decreases with an increase in E the capacity 0 is thus increased. Applying this reasoning to the condenser shown in the drawings it is apparent why, as stated above, the axial shifting of shaft 12 will be without balancing effect on the two condensers if. these are both mechanically identical as to the spacing of the plates. Moving the shaft axially will vary the eccentricity of spacing in each condenser, but will vary it equally in both. The capacities of both condensers are changed, but since they are changed equally and uniformly no balancing effect Wlll be produced. If, however, the condensers are unequal with respect to the spacing of the plates,that is, if the eccentricity of spacing in the two condensers is unequal numerically or, being numerically equal, are opposite in algebraic signthe vshift of the axis of the shaft will Vary the central plate is exactly in the middle and becoming greater numerically as the plate is shifted sideways.

Substituting these values of d and d in Equation (1) above, we have order to equalize the capacity of the two condensers, in other words, balance the two condensers, the shaft 12 is adjusted back and forth until it is observed that the two capacities are shown to be equal. Then shaft 12 is fixed in this adjusted position in the manner heretofore described.

Providing the plates of both condensers are all parallel as described an adjustment which balances both condensers in one rotative position will be equally eflective throughout the rotative range of the movable plates. As a check upon the parallelism ofthe plates; afterthe capacities have been adjusted to balance in one rotative position, comparative capacity readings may be taken with the movable plates rotated to several different positions. If then the capacities do not always agree the plates are not parallel and should be made so.

Obviously various changes and modifications in the detailed structure and arrangements of parts shown may be made without materially departing from the invention as hereinafter claimed.

What I claim is:

1. A multi-part variable condenser comprising a plurality of condenser units each composed of interleaved sets of fixed and movable plates with spaces between adjacent plates when interleaved, means for varying simultaneously the degree of interleaving of the sets in the several units to thereby adjust simultaneously the capacities of all the units, and means for varying the relation between the eccentricity of spacing of the interleaved sets of plates in each unit and the eccentricity of spacing in the other units.

2. A multi-part variable condenser comprising a plurality of condenser units each composed of interleaved fixed and movable plates with spaces between adjacent plates when interleaved, means for moving simultaneously the movable plates of all units into or out of interleaved relationwith their respective fixed plates, thereby to adjust simultaneously the individual capacities of the several condenser units, and means for varying the relation between the eccentricity of spacing of the interleaved sets of plates in each unit and the eccentricity of spacing in the other units. 7

3. A inulti-part variable condenser comprising a plurality of condenser units each composed of interleaved stator and rotor plates, the several units being normally in a condition of slight electrical unbalance, and means for adjusting the stator and rotor plates axially with respect to each other to bring the several units into electrical balance.

4. A tandem condenser comprising two condenser units each having a set of stator plates and a set of rotor plates interleaved with the stator plates, a rotatable shaft bearing all of the rotor plates in fixed spaced relation, the spacing of the rotor plates on the shaft being such that when the rotor plates of one set interleave centrally between their respective stator plates the rotor plates of the other set will be slightly unequally spaced between their respective stator plates, and means for adjusting the shaft axially with respect to the stator plates to bring the two condenser units into electrical balance. 5. A method of balancing electrically the several units of a gang condenser which coinprises changing the eccentricity of spacing of the interleaved plates of each unit relative to the eccentricity of spacing of the other units. In testimony whereof I have aifixed my signature.

CLARENCE" D. TUSKA. 

